Apparatus and method for producing ultrashort laser pulses

Abstract

The invention relates to a device (10) for producing ultrashort laser pulses, said device having features of claim 1, and to a method for producing ultrashort laser pulses, said method having features of the additional independent claim.

Description

[0001] Title: Device and method for generating ultrashort laser pulses

[0002] Description

[0003] The invention relates to a device for generating ultrashort laser pulses with features of claim 1 and a method for generating ultrashort laser pulses with features of the dependent claim.

[0004] Amplifying ultrashort laser pulses typically results in the undesired effect of "gain narrowing." To suppress this effect, the input laser pulses (seed laser pulses) can be spectrally preconditioned. The resulting spectral bandwidth of the laser pulses after amplification (output pulses) can thus be greater than it would be without preconditioning. US patent 9401580 describes such a method.

[0005] Typically, this preconditioning is achieved by a spectral filter, which selectively suppresses portions of the seed laser pulse spectrum that would otherwise be amplified disproportionately by the amplification medium, thus distorting the spectrum of the output pulses in an undesirable way.

[0006] Such filters can be achieved using static or variable filter elements. These include, for example, layer interference filters, fiber or volume Bragg gratings, spatially dispersive elements based on diffraction gratings or prisms, and acousto-optic filters.

[0007] Alternatively, a seed laser pulse spectrally shifted relative to the gain spectrum of the amplifier material can be used to achieve a similar effect. WO 2019 046 049 Al of fenbart describes such a method.

[0008] The production of interference filters based on layers or Bragg gratings is subject to large tolerances and can hardly be achieved without selection and scrap. Furthermore, there is a strong dependence on the angle of incidence, which complicates the adjustment. While implementing a filter based on spatially dispersive elements is adaptable, it is also associated with high adjustment effort and high component costs.

[0009] It is therefore an object of the present invention to provide a device and a method for generating ultrashort laser pulses, thereby eliminating the disadvantages mentioned above. The above object is achieved by a device for generating ultrashort laser pulses having the features of claim 1.

[0010] The device comprises a seed laser for generating seed laser pulses. The seed laser can be configured to generate laser pulses, in particular laser pulses with a spectral bandwidth that enables laser pulses shorter than 1 ps (picosecond). The seed laser can be configured as a fiber laser and / or a diode laser. The device also comprises at least one amplifier laser for amplifying the seed laser pulses. The amplifier laser can be configured as a disk, a plate, a rod, a slab, and / or a fiber. The device includes a filter for filtering the seed laser pulses. The device is configured such that the seed laser pulses pass through the filter before entering the amplifier laser. The filter is configured as a bulk absorbing filter that filters in a wavelength range that is to be amplified by the amplifier laser.The filter is specifically designed to filter a wavelength that is to be amplified by the amplifier laser. The filter is specifically designed as a resonant absorption filter. The filter is specifically configured for the spectral preconditioning of the seed laser pulses.

[0011] This allows for the spectral preconditioning of ultrashort laser pulses using simple means. The effect of gain narrowing can be avoided or at least reduced. Targeted coupling into or out of the filter is not necessary. In particular, there is no angular dependence. The device is therefore insensitive to adjustment. The filter can exhibit (almost) temperature-independent absorption behavior over a wide range. The device can be implemented in a very compact and space-saving manner and / or at a significantly lower cost compared to the prior art. In particular, the device can generate ultrashort laser pulses that are at least 10% shorter than would be the case without the device's filter.

[0012] According to a further development of the device, the filter can be doped. The amplifier laser can have an active medium. The dopant and the active medium can comprise the same material and / or be made of the same material. The dopant and the active medium can comprise the same chemical element and / or be made of the same chemical element.

[0013] The filter can be configured as an unpumped or non-inverted subvolume within a volume of the amplifier medium. In other words, the filter can be configured as an unpumped or non-inverted volume within the same portion of the amplifier medium. The filter can be integrated into the amplifier laser and / or configured as part of the amplifier laser or its amplifier medium.

[0014] Thus, the seed laser pulses can first be passed through a material that is spectroscopically similar or identical (a "resonant filter") before being amplified in the amplifier laser. Reabsorption at the laser wavelength can attenuate the central part of the seed laser pulse spectrum. This creates a "hole" or "dip" in the spectrum of the respective seed laser pulses. In the amplifier laser, this hole can then be filled by (spectrally) non-homogeneous amplification, resulting in a broader spectrum of the amplified seed laser pulses (output pulses) than would be the case without the filter.

[0015] This allows the filter wavelengths to be intrinsically matched to the emission spectrum of the amplifier material. No adjustment or calibration of the filter is necessary.

[0016] According to a further development of the device, the filter can include a host. The host can be configured as a host medium. The host can be configured as a crystalline structure or as a crystal. The host can include quantum dots, dye molecules, and / or lantanoid ions, in particular Yb (ytterbium), Er (erbium), Tm (thulium), and Nd (neodymium).

[0017] This allows the filter to be implemented as efficiently as possible using simple means.

[0018] According to a further development of the device, the host can be made of YAG (yttrium aluminum garnet), LuAG (lutetium aluminum garnet), KYW (potassium yttrium tungstate), Lu2O3 (lutetium oxide) and / or glass.

[0019] This allows the filter to be implemented as efficiently as possible using simple means. According to a further development of the device, the amplifier laser can be configured as a Yb:YAG, Yb:Lu2O3, or Yb:LuAG laser.

[0020] The filter can be (automatically) adapted to the respective medium of the amplifier laser. In particular, this means, for example, for Yb:YAG, that the absorption at room temperature and low inversion directly at the laser wavelength (1030 nm) is well adapted to the requirements of a spectral filter for suppressing gain narrowing.

[0021] In particular, if the amplifier laser is configured as a Yb:YAG laser, the filter can comprise or be formed from the material Yb:LuAG, Yb:YAG, or YbAG. The active medium of the amplifier laser can also comprise or be formed from other laser materials, especially Yb-doped ones. The filter material and / or the active material of the amplifier laser can be either a (single) crystal or a ceramic.

[0022] This allows the amplifier laser to be implemented as efficiently as possible using simple means.

[0023] By selecting parameters such as doping concentration and filter length, the "depth" of a desired central wavelength filter can be adjusted relative to the transmitted portions of the spectrum. It is particularly important to ensure that the amount of absorbed light does not lead to a significant inversion of the filter (or the resonant filter material), which would then become transparent and unable to absorb any more light. This can be achieved, for example, by appropriately selecting beam sizes. In particular, since the spectral preconditioning (in the filter) occurs before the amplification (in the amplifier laser), only small light powers can be involved, which, under suitable boundary conditions, do not contribute to significant inversion in the filter (or filter material).

[0024] Another way to adjust the spectral properties of the filter is temperature tuning, which can be used to influence the linewidth and absorption / emission in phononically broadened materials.

[0025] According to a further development of the device, the seed laser can be mode-locked.

[0026] This allows the seed laser to be implemented as efficiently as possible using simple means.

[0027] According to a further development of the device, the device can comprise an amplifier chain consisting of several amplifier lasers. The filter can be arranged in the laser beam direction upstream of one of the several amplifier lasers. In particular, the filter can be placed at any point in the amplifier chain.

[0028] This allows the device to be implemented flexibly with the most efficient amplification possible.

[0029] According to a further development of the device, the filter can be designed as a layer on a medium, in particular on the active medium of the amplifier laser. The filter can, in particular, be designed as a coating, especially of the active medium of the amplifier laser. This allows the filter to be implemented in a space-saving manner and with minimal sensitivity to misalignment.

[0030] According to a further development of the device, the device can comprise at least one optical isolator. The optical isolator can be arranged between any two components (such as a seed laser, amplifier laser, or filter) of the device.

[0031] This allows the device to be further optimized.

[0032] According to a further development of the device, the filter can have an antireflective coating on at least one of its surfaces. In particular, the filter can have an antireflective coating on each of its end surfaces (input and output surfaces of the seed laser pulses).

[0033] This minimizes transmission losses through the filter.

[0034] It is conceivable that an additional dispersive element could be incorporated into the amplifier chain, which compensates as much as possible for deviations from an ideal spectral phase in order to generate the shortest possible laser pulse. In particular, phase deviations arising from a nonlinear interaction of the spectrally preconditioned laser pulse with the materials passing through the laser system can be compensated. Such nonlinear interactions can also occur in CPA systems, or be tolerated to a certain extent to save costs and / or complexity in the compressor. Such a dispersive element can be arranged after the seed laser, i.e., before or after the resonant spectral filter. Such a dispersive element can be arranged between the seed laser and the amplifier laser. Such a dispersive element could, for example, be...It may be designed as a fiber Bragg grating and / or a fiber stretcher that compensates for dispersion of a higher order than the second order.

[0035] It is conceivable that the filter could comprise or consist of different materials with closely spaced emission and absorption lines. In other words, it is possible to combine different materials with closely spaced emission and absorption lines to obtain a filter with desired properties through spectral superposition. Thus, the filter can be composite.

[0036] The device can be configured as part of an fs (femtosecond) laser system or form an fs laser system.

[0037] The above problem is solved by a method for generating ultrashort laser pulses using a device according to the above descriptions with the features of the dependent claim.

[0038] The procedure includes the following steps:

[0039] Generating seed laser pulses using the seed laser.

[0040] Filtering the seed laser pulses using the filter. Amplifying the filtered seed laser pulses using the amplifier laser.

[0041] Regarding the advantages achievable with this method, reference is made to the relevant explanations concerning the device. The measures described in connection with the device and / or those explained below can be used to further develop the method.

[0042] According to a further development of the procedure, the process can include the following step:

[0043] Performing the procedure in an f s laser system (especially less than 1 ps) and / or in a CPA (Chirped Pulse Amplification) system.

[0044] Further features, details and advantages of the invention will become apparent from the wording of the claims and from the following description of exemplary embodiments with reference to the drawings. The drawings show:

[0045] Fig. 1 shows a schematic representation of a device for generating ultrashort laser pulses;

[0046] Fig. 2 schematically shows a diagram of a spectrally preconditioned and a spectrally non-preconditioned seed laser pulse before amplification by the device according to Figure 1 and

[0047] Fig. 3 schematically shows a diagram of a spectrally preconditioned and a spectrally non-preconditioned seed laser pulse after a

[0048] Reinforcement by the device according to Figure 1 .

[0049] Figure 1 shows a schematic representation of a device 10 for generating ultrashort laser pulses. The device 10 comprises a seed laser 12 for generating seed laser pulses. The device 10 also comprises at least one amplifier laser 14 for amplifying the seed laser pulses. The device 10 includes a filter 16 for filtering the seed laser pulses. Spectral preconditioning of the seed laser pulses can be implemented using the filter 16.

[0050] The device 10 is configured such that the seed laser pulses pass through the filter 16 before entering the amplifier laser 14. The filter 16 is arranged between the seed laser 12 and the amplifier laser 14.

[0051] Filter 16 is configured as a bulk absorbing filter. Filter 16 is specifically configured as a resonant filter. Filter 16 filters in a wavelength range that is to be amplified by amplifier laser 14. Filter 16 filters specifically at the wavelength that is to be amplified by amplifier laser 14.

[0052] The filter 16 may be doped. The amplifier laser 14 may be active. The dopant and the active medium may comprise or be formed from the same material, in particular the same chemical element. The filter 16 may comprise a host. The host may comprise quantum dots, dye molecules, and / or lantanoid ions, in particular Yb, Er, Tm, Nd.

[0053] The host can be in the form of a crystalline structure or a crystal. In particular, the host can be in the form of YAG, LuAG, KYW, Lu2O3 and / or glass.

[0054] The filter 16 can be formed as a layer (or coating) on ​​a medium, in particular on the active medium of the amplifier laser 14.

[0055] The filter 16 can have an antireflective coating on at least one of its surfaces. The antireflective coating can, in particular, be arranged on an input and / or output coupling surface of the filter 16, wherein the input and output surfaces are...

[0056] The coupling area for coupling the seed laser pulses into and out of the filter 16 is formed.

[0057] The amplifier laser 14 can be configured as a Yb : YAG, Yb : Lu2O3 or Yb : LuAG laser .

[0058] The Seedlaser 12 can be mode-locked.

[0059] The device 10 can comprise at least one optical isolator 18. The optical isolator 18 can be arranged at any position between any two components of the device 10.

[0060] The device 10 can be an amplifier chain consisting of several

[0061] The amplifier lasers 14 comprise. The filter 16 can be arranged, in particular at any point in the amplifier chain, in the laser beam direction upstream of one of the multiple amplifier lasers 14. The laser beam direction runs from top to bottom in Figure 1.

[0062] The device 10 can be configured as part of an f s laser system or form an f s laser system.

[0063] Figure 2 schematically shows a diagram of a spectrally preconditioned and a spectrally non-preconditioned seed laser pulse before amplification by the device 10 according to Figure 1.

[0064] Here, the wavelength in arbitrary units is shown on the x-axis 20 and the intensity in arbitrary units on the y-axis 22. Curve 24, represented by a solid line, describes a spectrum of a seed laser pulse without passing through filter 16 (spectrally unconditioned). In other words, the seed laser pulse represented by curve 24 was not filtered by filter 16.

[0065] Curve 26, represented by a dashed line, describes the spectrum of a seed laser pulse after passing through filter 16 (spectrally preconditioned). In other words, the seed laser pulse represented by curve 26 was filtered using filter 16.

[0066] By means of spectral preconditioning using the filter 16, (local) intensity minima are achieved in the individual seed laser pulses in a desired wavelength range or at a desired wavelength, which is to be amplified in the downstream amplifier laser 14. In other words, an "intensity dip" is achieved in a desired wavelength range or at a desired wavelength, which is to be amplified in the downstream amplifier laser 14.

[0067] Figure 3 schematically shows a diagram of a spectrally preconditioned and a spectrally non-preconditioned seed laser pulse after amplification by the device 10 according to Figure 1.

[0068] Here too, the wavelength in arbitrary units is shown on the X-axis 20 and the intensity in arbitrary units is shown on the Y-axis 22.

[0069] Curve 28, represented by a solid line, describes the spectrum of a seed laser pulse amplified by amplifier laser 14 but not spectrally preconditioned. In other words, the seed laser pulse represented by curve 28 has not been filtered by filter 16.

[0070] Curve 30, represented by a dashed line, describes the spectrum of a seed laser pulse amplified by amplifier laser 14 and spectrally preconditioned by filter 16. In other words, the seed laser pulse represented by curve 30 has been filtered by filter 16.

[0071] By using the spectral preconditioning filter 16, the spectra of the individual seed laser pulses can be broadened. In other words, the spectral bandwidth of the amplified seed laser pulses can be increased. This allows for the subsequent generation of shorter laser pulses. In particular, at least 10% shorter laser pulses can be generated with the spectral preconditioning filter 16 than without it.

[0072] The following describes a method for generating ultrashort laser pulses using a device as described above, with reference to Figures 1 to 3. The device may be the device 10 shown in Figure 1.

[0073] The procedure includes the following steps:

[0074] Generating seed laser pulses using the seed laser 12 .

[0075] Filtering the seed laser pulses using filter 16.

[0076] Amplification of the filtered seed laser pulses using the amplifier laser 14 .

[0077] The procedure may include the following step:

[0078] Performing the procedure in an f s laser system and / or in a CPA system.

Claims

Patent claims 1. Device (10) for generating ultrashort laser pulses comprising: a seed laser (12) for generating seed laser pulses, at least one amplifier laser (14) for amplifying the seed laser pulses, a filter (16) for filtering the seed laser pulses, wherein the device (10) is configured such that the seed laser pulses pass through the filter (16) before entering the amplifier laser (14), wherein the filter (16) is designed as a volume absorbing filter that filters in a wavelength range which is to be amplified by the amplifier laser (14).

2. Device (10) according to claim 1, characterized in that the filter (16) has a doping and the amplifier laser (14) has an active medium, wherein the doping and the active medium may comprise the same material, in particular the same chemical element, and in particular are formed from the same material, in particular from the same chemical element.

3. Device (10) according to claim 1 or 2, characterized in that the filter (16) comprises a host, wherein the host comprises quantum dots, dye molecules and / or lantanoid ions, in particular Yb, Er, Tm, Nd.

4. Device (10) according to the preceding claim, characterized in that the host is designed as YAG, LuAG, KYW, Lu2O3 and / or glass.

5. Device (10) according to one of the preceding claims, characterized in that the amplifier laser (14) is designed as a Yb:YAG, Yb:Lu2O3 or Yb:LuAG laser.

6. Device (10) according to one of the preceding claims, characterized in that the seed laser (12) is mode-linked.

7. Device (10) according to one of the preceding claims, characterized in that the device (10) comprises an amplifier chain consisting of several amplifier lasers (14), in particular wherein the filter (16) is arranged in the direction of the laser beam in front of one of the several amplifier lasers (14).

8. Device (10) according to one of the preceding claims, characterized in that the filter (16) is formed as a layer on a medium.

9. Device (10) according to one of the preceding claims, characterized in that the device (10) comprises at least one optical insulator (18).

10. Device (10) according to one of the preceding claims, characterized in that the filter (16) has an anti-reflective coating on at least one of its surfaces.

11. Method for generating ultrashort laser pulses using a device according to one of the preceding Claims, characterized by the steps: Generating seed laser pulses using the seed laser (12) ; Filtering the seed laser pulses using the filter (16) ; Amplification of the filtered seed laser pulses using the amplifier laser (14) .

12. Method according to the preceding claim, characterized by the step of: - performing the method in an f s laser system and / or in a CPA system.

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